1. Field of the Invention
This invention relates to integrated circuit structures and in particular to a self-aligned antiblooming structure for individual elements of a charge-coupled device image sensor.
2. Description of the Prior Art
The phenomenon in charge-coupled device (CCD) image sensors in which excess signal charge from saturated sensor elements spills into adjacent sensor elements or shift registers is known as blooming. When this excess charge spills into an adjacent shift register, it generally mixes with the signal charge from a large number of pixels, thereby causing a particularly objectionable type of blooming. This type of blooming produces a vertical streak in the image wherever a saturated pixel occurs.
Structures in image sensors which prevent or limit blooming are known as antiblooming structures. The most complete blooming prevention requires an antiblooming structure at each sensor element so that the individual elements cannot bloom. This function has been referred to as element antiblooming to distinguish it from the much less effective prior art column antiblooming function which limits blooming to the vertical column in which the saturated elements occurs. No prior art element antiblooming structures are known to applicants.